Processes for subjecting propylene or isobutlyene to the vapor-phase catalytic oxidation or the vapor-phase catalytic ammoxidation so as to produce the corresponding unsaturated carboxylic acid or unsaturated nitrile have been well known from hitherto. In recent years, processes for subjecting propane or isobutane instead of propylene or isobutlyene to the vapor-phase catalytic oxidation or the vapor-phase catalytic ammoxidation so as to produce the corresponding unsaturated carboxylic acid or unsaturated nitrile have attracted attention, and various catalysts and reaction processes have been proposed.
For example, oxide catalysts containing Mo—V—Nb—Sb or Mo—V—Nb—Te have been disclosed in Patent Document 1 (WO 01/096016), Patent Document 2 (Japanese Patent Application Laid-open No. 2004-148302), Patent Document 3 (Japanese Patent Application Laid-open No. 10-28862), Patent Document 4 (Japanese Patent Application Laid-open No. 2002-239382), Patent Document 5 (Japanese Patent Application Laid-open No. 11-253801), Patent Document 6 (Japanese Patent Application Laid-open No. 07-315842) and Patent Document 7 (Japanese Patent Application Laid-open No. 2001-206870). Of these patent documents, for example in Patent Document 1 (WO 01/096016), it is stated that a specified element (Al or W) for which the element and/or an oxide thereof forms a rutile-like structure may be contained in the Mo—V—Nb—Te or Mo—V—Nb—Sb. However, the main composition of oxide catalysts actually disclosed is Mo—V—Nb—Sb—Ti or Mo—V—Nb—Sb—Al, and the yield therefor is still insufficient.
Moreover, in Patent Document 2 (Japanese Patent Application Laid-open No. 2004-148302), there is described an example in which acrylic acid is obtained from propane using a catalyst obtained by subjecting a mixture of tellurium dioxide and ammonium heptamolybdate to hydrothermal treatment for 1.5 hours at 100° C., adding manganese (II) nitrate, vanadyl sulfate hydrate and ammonium niobium oxalate while stirring, and subjecting to hydrothermal treatment for 4 days at 175° C. However, a sufficient acrylic acid yield is still not exhibited. In addition, when preparing the catalyst, hydrothermal treatment for a prolonged period of time at a high temperature is required, and many steps including pressurization, filtration, washing and drying are required, and hence the operational process is complex, and thus there is a problem that industrialization is accompanied by difficulties.
When carrying out the vapor-phase catalytic oxidation/ammoxidation industrially, it is important to maintain a high yield for a prolonged period of time. In Patent Document 3 (Japanese Patent Application Laid-open No. 10-28862), there is disclosed an example in which W, a rare earth element, and an alkaline earth metal or the like are impregnated into a catalyst having a main composition of Mo—V—Nb—Te, whereby a high yield can be obtained. However, Te contained in the catalyst evaporates during reaction, and hence it is difficult to maintain a high yield over a prolonged period of time. Moreover, the yield for a Mo—V—Nb—Sb system is still low, and hence there is no disclosure regarding achieving both good yield and good lifetime simultaneously.
In the other patent documents, for example Patent Document 4 (Japanese Patent Application Laid-open No. 2002-239382), Patent Document 5 (Japanese Patent Application Laid-open No. 11-253801), Patent Document 6 (Japanese Patent Application Laid-open No. 07-315842) and Patent Document 7 (Japanese Patent Application Laid-open No. 2001-206870), use of manganese (Mn) or tungsten (W) is described, but the reaction results are still insufficient.
Patent Document 1: WO 01/096016
Patent Document 2: Japanese Patent Application Laid-open No. 2004-148302
Patent Document 3: Japanese Patent Application Laid-open No. 10-28862
Patent Document 4: Japanese Patent Application Laid-open No. 2002-239382)
Patent Document 5: Japanese Patent Application Laid-open No. 11-253801
Patent Document 6: Japanese Patent Application Laid-open No. 07-315842)
Patent Document 7: Japanese Patent Application Laid-open No. 2001-206870